Install mypy only in travis tests, not generally in test dependencies, as it requires Py3.

.travis.yml

@@ -103,5 +103,6 @@ script:
   - PYTHON_DBG="python$( python -c 'import sys; print("%d.%d" % sys.version_info[:2])' )-dbg"
   - if $PYTHON_DBG -V >&2; then CFLAGS="-O0 -ggdb" $PYTHON_DBG runtests.py -vv Debugger --backends=$BACKEND; fi
   - if [ "$BACKEND" = "cpp" -a -n "${TRAVIS_PYTHON_VERSION##2.6*}" ]; then pip install pythran; fi
+  - if [ "$BACKEND" = "c" -a -n "${TRAVIS_PYTHON_VERSION##2*}" ]; then pip install mypy; fi
   - CFLAGS="-O2 -ggdb -Wall -Wextra $(python -c 'import sys; print("-fno-strict-aliasing" if sys.version_info[0] == 2 else "")')" python setup.py build_ext -i
   - CFLAGS="-O0 -ggdb -Wall -Wextra" python runtests.py -vv -x Debugger --backends=$BACKEND -j7

test-requirements.txt

 numpy
 jupyter
 coverage
-mypy